Does grit out-weigh IQ? Massive UK study shows not

Some research has shown small associations between “grit” and academic achievement. These have been from small, selected samples, but the results have been widely cited as showing that “Grit outweighs IQ”. What do large, well controlled studies suggest?
A new paper from the lab of lifetime awardee Robert Plomin and written by 2014 prize winner Kaili Rimfeld, data from  4,500 16-year-old twins show that grit predicted just one half of one percent (0.5%) of variance in high-stakes school results. This was dwarfed by the effects of IQ. Conscientiousness and other dimensions of personality accounted for about 12 times the effect of grit.
The results appear in the leading journal Journal of Personality and Social Psychology.